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Question
Describe two anomalies of Mendeleev's periodic classification of elements.
Solution
Anomalies of Mendeleev's periodic classification of elements:
1. Mendeleev's periodic classification of elements could not explain the position of isotopes in the periodic table: Since, isotopes of the same metal have similar chemical properties but different in their atomic masses. So, the isotopes of the same element should be given different place in periodic table as Mendeleev's periodic table was arranged in increasing order of their atomic masses. However, isotopes were not given separate place in his periodic table.
2.Mendeleev's periodic classification of elements could not assign a proper place for the element,hydrogen. Since, hydrogen resembled both alkali metals and halogens in some of the properties.
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The correct formula of the oxide of Eka-aluminium element predicted by Mendeleev was:
(a) EaO3
(b) Ea3O2
(c) Ea2O3
(d) EaO
Match the columns.
| Column A | Column B |
| 1) Eka-aluminium | a) Scandium |
| 2) Eka-Silicon | b) Gallium |
| 3) Eka- boron | c) Germanium |
| d) Beryllium |
Write the name.
The family of group 1 elements.
Write the name.
The family of elements having zero valency.
Match the column:
| Column ‘A’ | Column ‘B’ |
| Alkali metals | (a) Group 18 |
| Halogens | (b) Group 1 |
| Noble gases | (c) Group 17 |
